ResearchPad - hypoxia https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Levosimendan reduces segmental pulmonary vascular resistance in isolated perfused rat lungs and relaxes human pulmonary vessels]]> https://www.researchpad.co/article/elastic_article_15739 Levosimendan is approved for acute heart failure. Within this context, pulmonary hypertension represents a frequent co-morbidity. Hence, the effects of levosimendan on segmental pulmonary vascular resistance (PVR) are relevant. So far, this issue has been not studied. Beyond that the relaxant effects of levosimendan in human pulmonary vessel are unknown. We addressed these topics in rats’ isolated perfused lungs (IPL) and human precision-cut lung slices (PCLS).Material and methodsIn IPL, levosimendan (10 μM) was perfused in untreated and endothelin-1 pre-contracted lungs. The pulmonary arterial pressure (PPA) was continuously recorded and the capillary pressure (Pcap) was determined by the double-occlusion method. Thereafter, segmental PVR, expressed as precapillary (Rpre) and postcapillary resistance (Rpost) and PVR were calculated. Human PCLS were prepared from patients undergoing lobectomy. Levosimendan-induced relaxation was studied in naïve and endothelin-1 pre-contracted PAs and PVs. In endothelin-1 pre-contracted PAs, the role of K+-channels was studied by inhibition of KATP-channels (glibenclamide), BKCa2+-channels (iberiotoxin) and Kv-channels (4-aminopyridine). All changes of the vascular tone were measured by videomicroscopy. In addition, the increase of cAMP/GMP due to levosimendan was measured by ELISA.ResultsLevosimendan did not relax untreated lungs or naïve PAs and PVs. In IPL, levosimendan attenuated the endothelin-1 induced increase of PPA, PVR, Rpre and Rpost. In human PCLS, levosimendan relaxed pre-contracted PAs or PVs to 137% or 127%, respectively. In pre-contracted PAs, the relaxant effect of levosimendan was reduced, if KATP- and Kv-channels were inhibited. Further, levosimendan increased cGMP in PAs/PVs, but cAMP only in PVs.DiscussionLevosimendan reduces rats’ segmental PVR and relaxes human PAs or PVs, if the pulmonary vascular tone is enhanced by endothelin-1. Regarding levosimendan-induced relaxation, the activation of KATP- and Kv-channels is of impact, as well as the formation of cAMP and cGMP. In conclusion, our results suggest that levosimendan improves pulmonary haemodynamics, if PVR is increased as it is the case in pulmonary hypertension. ]]> <![CDATA[Serum glutamate dehydrogenase activity enables early detection of liver injury in subjects with underlying muscle impairments]]> https://www.researchpad.co/article/elastic_article_14604 Serum activities of alanine and aspartate aminotransferases (ALT and AST) are used as gold standard biomarkers for the diagnosis of hepatocellular injury. Since ALT and AST lack liver specificity, the diagnosis of the onset of hepatocellular injury in patients with underlying muscle impairments is severely limited. Thus, we evaluated the potential of glutamate dehydrogenase (GLDH) as a liver specific alternative biomarker of hepatocellular injury. In our study, serum GLDH in subjects with Duchene muscular dystrophy (DMD) was equivalent to serum GLDH in age matched healthy subjects, while serum ALT was increased 20-fold in DMD subjects. Furthermore, serum GLDH in 131 subjects with variety of muscle impairments was similar to serum GLDH of healthy subjects while serum ALT corelated with serum creatine kinase, a widely accepted biomarker of muscle impairment. In addition, significant elevations of ALT, AST, and CK were observed in a case of a patient with rhabdomyolysis, while serum GLDH stayed within the normal range until the onset of hypoxia-induced liver injury. In a mouse model of DMD (DMDmdx), serum GLDH but not serum ALT clearly correlated with the degree of acetaminophen-induced liver injury. Taken together, our data support the utility of serum GLDH as a liver-specific biomarker of liver injury that has a potential to improve diagnosis of hepatocellular injury in patients with underlying muscle impairments. In drug development, GLDH may have utility as a biomarker of drug induced liver injury in clinical trials of new therapies to treat muscle diseases such as DMD.

]]>
<![CDATA[Citrate lyase CitE in Mycobacterium tuberculosis contributes to mycobacterial survival under hypoxic conditions]]> https://www.researchpad.co/article/N5c16b8fb-2363-48af-bce8-dbbca8329b25

Mycobacterium tuberculosis is the causative agent of tuberculosis and has evolved an ability to survive in hostile host environments. M. tuberculosis is thought to utilize the rTCA cycle to sustain its latent growth during infection, but the enzymatic characteristics and physiological function for the key citrate lyase of the rTCA cycle, MtbCitE, in the important pathogen remain unclear. In this study, we investigated the function of MtbCitE based on its structural properties and sequence comparisons with other bacterial citrate lyase subunits. We showed that several amino acid residues were important for the citrate cleavage activity of MtbCitE. Strikingly, the citrate cleavage activity of MtbCitE was inhibited by ATP, indicating that energy metabolism might couple with the regulation of MtbCitE activity, which differed from other CitEs. More interestingly, deletion of citE from Mycobacterium bovis BCG decreased the mycobacterial survival rate under hypoxic conditions, whereas complementation with citE restored the phenotype to wild-type levels. Consistently, three key rTCA cycle enzymes were positively regulated under hypoxic conditions in mycobacteria. Therefore, we characterized a unique citrate lyase MtbCitE from M. tuberculosis and found that the CitE protein significantly contributed to mycobacterial survival under hypoxic conditions.

]]>
<![CDATA[The sensitivity to Hsp90 inhibitors of both normal and oncogenically transformed cells is determined by the equilibrium between cellular quiescence and activity]]> https://www.researchpad.co/article/5c648d48d5eed0c484c8243f

The molecular chaperone Hsp90 is an essential and highly abundant central node in the interactome of eukaryotic cells. Many of its large number of client proteins are relevant to cancer. A hallmark of Hsp90-dependent proteins is that their accumulation is compromised by Hsp90 inhibitors. Combined with the anecdotal observation that cancer cells may be more sensitive to Hsp90 inhibitors, this has led to clinical trials aiming to develop Hsp90 inhibitors as anti-cancer agents. However, the sensitivity to Hsp90 inhibitors has not been studied in rigorously matched normal versus cancer cells, and despite the discovery of important regulators of Hsp90 activity and inhibitor sensitivity, it has remained unclear, why cancer cells might be more sensitive. To revisit this issue more systematically, we have generated an isogenic pair of normal and oncogenically transformed NIH-3T3 cell lines. Our proteomic analysis of the impact of three chemically different Hsp90 inhibitors shows that these affect a substantial portion of the oncogenic program and that indeed, transformed cells are hypersensitive. Targeting the oncogenic signaling pathway reverses the hypersensitivity, and so do inhibitors of DNA replication, cell growth, translation and energy metabolism. Conversely, stimulating normal cells with growth factors or challenging their proteostasis by overexpressing an aggregation-prone sensitizes them to Hsp90 inhibitors. Thus, the differential sensitivity to Hsp90 inhibitors may not stem from any particular intrinsic difference between normal and cancer cells, but rather from a shift in the balance between cellular quiescence and activity.

]]>
<![CDATA[Impact of moderate to severe obstructive sleep apnea on the cognition in idiopathic pulmonary fibrosis]]> https://www.researchpad.co/article/5c5df31bd5eed0c484580d2d

Introduction

Idiopathic pulmonary fibrosis (IPF) is a relentlessly progressive lung disease with a fatal prognosis to whose rapid evolution multiple comorbidities may contribute, one of the most common being obstructive sleep apnea (OSA). There are several potential factors and conditions for the emergence of a cognitive deficit in relation to IPF or associated morbidities.

Objectives

The goals of this study were to assess cognition in patients with IPF in stable phase and to identify clinical cognition modifiers.

Methods

In a cross-sectional study, 23 patients with IPF were evaluated using Montreal Cognitive Assessment (MoCA), an instrument for detecting mild cognitive impairments and were screened for OSA through overnight cardiorespiratory polygraphy and for anxiety and depression with three specific scale (Generalized Anxiety Disorder 7-item scale: GAD-7; the Patient Health Questionnaire: PHQ-9; Hospital Anxiety and Depression Scale: HADS).

Results

MoCA score was lower in patients with IPF when compared to controls subjects (24 [21,26] vs. 27 [26,28], p = 0.003) but not as significantly as in COPD patients (21 [18.8,23.3], p<0.0001). OSA was diagnosed in 19 (82.6%) IPF patients, 12 patients showed the presence of moderate-severe forms (63.15%). IPF patients with cognitive impairment (MoCA<23) exhibit a higher severity of OSA (apneea hypopnea index–AHI: 33.0±19.1 vs. 12.44±8.2, p = 0.018), and a higher Epworth score (7.1±3.3 vs. 4.3±1.8, p = 0.013). Anxiety and depression scores were not correlated with MoCA results.

Conclusions

Impaired cognition in patients with IPF is mild and affect the areas of visuospatial abilities, language and working memory. OSA could be a possible predictor of IPF cognition deficit. Given the high prevalence of multiple types of sleep disorders in IPF patients, these should be investigated at least by cardiorespiratory polygraphy.

]]>
<![CDATA[Nitrogen gas produces less behavioural and neurophysiological excitation than carbon dioxide in mice undergoing euthanasia]]> https://www.researchpad.co/article/5c5ca2bcd5eed0c48441e9d5

Carbon dioxide (CO2) is one of the most commonly used gas euthanasia agents in mice, despite reports of aversion and nociception. Inert gases such as nitrogen (N2) may be a viable alternative to carbon dioxide. Here we compared behavioural and electrophysiological reactions to CO2 or N2 at either slow fill or rapid fill in C57Bl/6 mice undergoing gas euthanasia. We found that mice euthanised with CO2 increased locomotor activity compared to baseline, whereas mice exposed to N2 decreased locomotion. Furthermore, mice exposed to CO2 showed significantly more vertical jumps and freezing episodes than mice exposed to N2. We further found that CO2 exposure resulted in increased theta:delta of the EEG, a measure of excitation, whereas the N2 decreased theta:delta. Differences in responses were not oxygen-concentration dependent. Taken together, these results demonstrate that CO2 increases both behavioural and electrophysiological excitation as well as producing a fear response, whereas N2 reduces behavioural activity and central neurological depression and may be less aversive although still produces a fear response. Further studies are required to evaluate N2 as a suitable euthanasia agent for mice.

]]>
<![CDATA[The influence of sleep apnea syndrome and intermittent hypoxia in carotid adventitial vasa vasorum]]> https://www.researchpad.co/article/5c63397cd5eed0c484ae689b

Subjects with sleep apnea-hypopnea syndrome (SAHS) show an increased carotid intima-media thickness. However, no data exist about earlier markers of atheromatous disease, such as the proliferation and expansion of the adventitial vasa vasorum (VV) to the avascular intima in this setting. Our aim was to assess carotid VV density and its relationship with sleep parameters in a cohort of obese patients without prior vascular events. A total of 55 subjects evaluated for bariatric surgery were prospectively recruited. A non-attended respiratory polygraphy was performed. The apnea-hypopnea index (AHI) and the cumulative percentage of time spent with oxygen saturation below 90% (CT90) were assessed. Serum concentrations of soluble intercellular adhesion molecule 1, P-selectin, lipocalin-2 and soluble vascular cell adhesion molecule 1 (sVCAM-1) were measured. Contrast-enhanced carotid ultrasound was used to assess the VV density. Patients with SAHS (80%) showed a higher adventitial VV density (0.801±0.125 vs. 0.697±0.082, p = 0.005) and higher levels of sVCAM-1 (745.2±137.8 vs. 643.3±122.7 ng/ml, p = 0.035) than subjects with an AHI lower than 10 events/hour. In addition, a positive association exist between mean VV density and AHI (r = 0.445, p = 0.001) and CT90 (r = 0.399, p = 0.005). Finally, in the multiple linear regression analysis, female sex, fasting plasma glucose and AHI (but not CT90) were the only variables independently associated with the mean adventitial VV density (R2 = 0.327). In conclusion, a high VV density is present in obese subjects with SAHS, and chronic intermittent hypoxia is pointed as an independent risk factor for the development of this early step of atheromatous disease.

]]>
<![CDATA[Intervention against hypertension in the next generation programmed by developmental hypoxia]]> https://www.researchpad.co/article/5c50c477d5eed0c4845e87d3

Evidence derived from human clinical studies and experimental animal models shows a causal relationship between adverse pregnancy and increased cardiovascular disease in the adult offspring. However, translational studies isolating mechanisms to design intervention are lacking. Sheep and humans share similar precocial developmental milestones in cardiovascular anatomy and physiology. We tested the hypothesis in sheep that maternal treatment with antioxidants protects against fetal growth restriction and programmed hypertension in adulthood in gestation complicated by chronic fetal hypoxia, the most common adverse consequence in human pregnancy. Using bespoke isobaric chambers, chronically catheterized sheep carrying singletons underwent normoxia or hypoxia (10% oxygen [O2]) ± vitamin C treatment (maternal 200 mg.kg−1 IV daily) for the last third of gestation. In one cohort, the maternal arterial blood gas status, the value at which 50% of the maternal hemoglobin is saturated with oxygen (P50), nitric oxide (NO) bioavailability, oxidative stress, and antioxidant capacity were determined. In another, naturally delivered offspring were raised under normoxia until early adulthood (9 months). Lambs were chronically instrumented and cardiovascular function tested in vivo. Following euthanasia, femoral arterial segments were isolated and endothelial function determined by wire myography. Hypoxic pregnancy induced fetal growth restriction and fetal oxidative stress. At adulthood, it programmed hypertension by enhancing vasoconstrictor reactivity and impairing NO-independent endothelial function. Maternal vitamin C in hypoxic pregnancy improved transplacental oxygenation and enhanced fetal antioxidant capacity while increasing NO bioavailability, offsetting constrictor hyper-reactivity and replenishing endothelial function in the adult offspring. These discoveries provide novel insight into mechanisms and interventions against fetal growth restriction and adult-onset programmed hypertension in an animal model of complicated pregnancy in a species of similar temporal developmental milestones to humans.

]]>
<![CDATA[Melatonin: The smart molecule that differentially modulates autophagy in tumor and normal placental cells]]> https://www.researchpad.co/article/5c40f7abd5eed0c484386589

Melatonin has protective roles in normal cells and cytotoxic actions in cancer cells, with effects involving autophagy and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor pathways. Hypoxia/reoxygenation (H/R) induces oxidative damage and apoptosis. These consequences activate autophagy, which degrades damaged cellular content, as well as activates Nrf2 the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor, and thereby the expression of protective genes. Melatonin has protective roles in normal cells and cytotoxic actions in cancer cells, with effects involving autophagy and Nrf2 pathways. The current study shows melatonin to differentially modulate autophagy and Nrf2 pathways in tumor and normal placental cells exposed to H/R. BeWo, a human placental choriocarcinoma cell line, and primary villous cytotrophoblasts isolated from normal term placenta, were maintained in normoxia (8% O2) for 24 h or exposed to hypoxia (0.5% of O2 for 4 h) followed by 20 h of normoxia, creating a situation of H/R, in the presence or absence of 1 mM melatonin. Melatonin induced a 7-fold increase in the activation of 5' adenosine monophosphate-activated protein kinase (AMPK)α, an upstream modulator of autophagy, rising to a 16-fold increase in BeWo cells co-exposed to H/R and melatonin, compared to controls. H/R induced autophagosome formation via the increased expression of Beclin-1 (by 94%) and ATG7 (by 97%) in BeWo cells. Moreover, H/R also induced autophagic activity, indicated by the by the 630% increase in P62, and increased Nrf2 by 314% in BeWo cells. In H/R conditions, melatonin reduced autophagic activity by 74% and Nrf2 expression activation by 300%, leading to BeWo cell apoptosis. In contrast, In human primary villous cytotrophoblasts, H/R induced autophagy and Nrf2, which melatonin further potentiated, thereby affording protection against H/R. This study demonstrates that melatonin differentially modulates autophagy and the Nrf2 pathway in normal vs. tumor trophoblast cells, being cytoprotective in normal cells whilst increasing apoptosis in tumoral trophoblast cells.

]]>
<![CDATA[Sildenafil does not improve performance in 16.1 km cycle exercise time-trial in acute hypoxia]]> https://www.researchpad.co/article/5c605a97d5eed0c4847cd2ae

Sildenafil is a pulmonary vasodilator that has potential to mitigate the decrement in endurance performance caused by hypoxic pulmonary vasoconstriction. The purpose of this study was to determine the effects of sildenafil on pulmonary artery pressure, cardiac output, pulse oxygen saturation, and exercise performance at moderate simulated altitude. We hypothesized that sildenafil would reduce the decline in exercise performance in hypoxia by blunting the rise in pulmonary artery pressure and causing a relative increase in cardiac output and oxygen saturation. Twelve endurance trained men performed three experimental cycling trials at sea level and simulated moderate altitude of 3,000m (FIO2 = 0.147) after ingesting either a placebo or sildenafil 50 mg capsule in a double blinded fashion. Each test consisted of a warmup period, a 15-minute steady state period at 60% of peak power output, and a 16.1 km time-trial. All subjects experienced a decline in maximal exercise capacity in hypoxia that ranged from 6% to 24%. This decline was correlated with the reduction in pulse oxygen saturation in hypoxic maximal exercise. Sildenafil had no effect on pulmonary artery pressure, cardiac output, or pulse oxygen saturation measured during steady state exercise. There was no effect of sildenafil on mean power output during the time-trial. During high intensity cycle exercise in acute, moderate hypoxia pulmonary artery pressure is unaffected by sildenafil and does not appear to influence cardiovascular function or exercise performance.

]]>
<![CDATA[Insights on the impact of mitochondrial organisation on bioenergetics in high-resolution computational models of cardiac cell architecture]]> https://www.researchpad.co/article/5c117ba4d5eed0c484699f6e

Recent electron microscopy data have revealed that cardiac mitochondria are not arranged in crystalline columns but are organised with several mitochondria aggregated into columns of varying sizes spanning the cell cross-section. This raises the question—how does the mitochondrial arrangement affect the metabolite distributions within cardiomyocytes and what is its impact on force dynamics? Here, we address this question by employing finite element modeling of cardiac bioenergetics on computational meshes derived from electron microscope images. Our results indicate that heterogeneous mitochondrial distributions can lead to significant spatial variation across the cell in concentrations of inorganic phosphate, creatine (Cr) and creatine phosphate (PCr). However, our model predicts that sufficient activity of the creatine kinase (CK) system, coupled with rapid diffusion of Cr and PCr, maintains near uniform ATP and ADP ratios across the cell cross sections. This homogenous distribution of ATP and ADP should also evenly distribute force production and twitch duration with contraction. These results suggest that the PCr shuttle and associated enzymatic reactions act to maintain uniform force dynamics in the cell despite the heterogeneous mitochondrial organization. However, our model also predicts that under hypoxia activity of mitochondrial CK enzymes and diffusion of high-energy phosphate compounds may be insufficient to sustain uniform ATP/ADP distribution and hence force generation.

]]>
<![CDATA[Individual and combined effects of low dissolved oxygen and low pH on survival of early stage larval blue crabs, Callinectes sapidus]]> https://www.researchpad.co/article/5c141eded5eed0c484d289a2

A large number of coastal ecosystems globally are subjected to concurrent hypoxic and acidified conditions that will likely intensify and expand with continued climate change. In temperate regions, the spawning of many important organisms including the Atlantic blue crab Callinectes sapidus occurs during the summer months when the severity of coastal hypoxia and acidification is the greatest. While the blue crab earliest larval stage can be exposed to co-occurring hypoxia and acidification observed in many coastal ecosystems, the effects of these concurrent stressors on larval blue crab survival is unknown. This study investigated the individual and combined consequences of low dissolved oxygen (DO) and low pH on blue crab larvae survival through a series of short-term experiments. During 14-day experiments with moderately hypoxic conditions (117–127 μM O2 or 3.74–4.06 mg L-1) and acidified conditions (pH on total scale of 7.16–7.33), low DO and low pH individually and significantly reduced larval survival by 60% and 49%, respectively, with the combination of stressors reducing survival by 87% compared to the control treatment (210–269 μM O2 or 6.72–8.61 mg L-1, 7.91–7.94 DO and pH, respectively). During 4-day experiments with lower DO levels (68–83 μM O2 or 2.18–2.62 mg L-1) and comparable pH levels of 7.29–7.39, low DO individually reduced survival by >90% compared to the control (261–267 μM O2 or 8.35–8.54 mg L-1, 7.92–7.97 DO and pH, respectively), whereas low pH had no effect and there was no interaction between stressors. Over a 4-day period, the DO threshold at which 50% of the larval blue crab population died (LC50) was 121 μM O2 (3.86 mgL-1). In 14-day experiments, the DO and pH effects were additive, yielding survival rates lower than the individual treatments, and significantly correlated with DO and pH concentrations. Collectively, these findings indicate that blue crab sensitivity to both low DO and low pH are acute within the larval stage, depend on the intensity and duration of exposure, and leads to mortality, thereby potentially contributing to the interannual variability and possible regional declines of this fishery.

]]>
<![CDATA[Modeling the effects of atmospheric pressure on suicide rates in the USA using geographically weighted regression]]> https://www.researchpad.co/article/5c117b58d5eed0c484698c77

Low atmospheric pressure may increase depression and suicide through inducing hypoxia. Previous studies have not evaluated the geographic variation of this relationship across the United States. Analyses were based on three groupings of age-adjusted completed suicide rates (all suicide, firearm-related suicide, non-firearm-related suicide) from 2286 counties in the United States. Multiple regression was used to determine the overall relationship between atmospheric pressure and completed suicide rates. Geographically weighted regression (GWR) models were used to obtain local coefficient estimates. A negative correlation between atmospheric pressure and completed suicide rates was observed for all three suicide groupings (p-value <0.0001). Significant, negative GWR coefficient estimates were located in the West and Northeast for the all suicides and firearm-related suicides, and in the Midwest for non-firearm-related suicides.

]]>
<![CDATA[Effects of acute hypoxia exposure with different durations on activation of Nrf2-ARE pathway in mouse skeletal muscle]]> https://www.researchpad.co/article/5c10287dd5eed0c4842474bf

Background

Hypoxia training enhances the endurance capacity of athletes. This response may in part be attributed to the hypoxia-induced increase in antioxidant capacity in skeletal muscles. Nuclear factor erythroid 2-related factor 2 (Nrf2), a key transcription factor which regulates the expression of genes via binding to the antioxidant-response element (ARE) of these genes, plays a crucial role in stimulating the body’s defense system and potentially responds to hypoxia. Meanwhile, hypoxia-inducible factor-1α (HIF-1α) is an important player in protecting cells from hypoxic stress. The purpose of this study was to investigate the effects of acute hypoxia exposure with different durations on the activation of Nrf2-ARE pathway and a possible regulatory role of HIF-1α in these responses.

Methods

C57BL/6J mice were allocated into the non-hypoxia 0-hour, 6-hour, 24-hour, and 48-hour hypoxic exposure (11.2% oxygen) groups. The quadriceps femoris was collected immediately after hypoxia. Further, to investigate the possible role of HIF-1α, C2C12 myoblasts with HIF-1α knockdown by small interfering RNA (siRNA) and the inducible HIF-1α transgenic mice were employed.

Results

The results showed that 48-hour hypoxia exposure up-regulated protein expression of Nrf2, Nrf2/ARE binding activity and the transcription of antioxidative genes containing ARE (Sod1 and others) in mouse skeletal muscle. Moreover, HIF-1α siRNA group of C2C12 myoblasts showed a remarkable inhibition of Nrf2 protein expression and nuclear accumulation in hypoxia exposure for 72 hours compared with that in siRNA-Control group of the cells. In addition, HIF-1α transgenic mice gave higher Nrf2 protein expression, Nrf2/ARE binding activity and expressions of Nrf2-mediated antioxidative genes in their skeletal muscle, compared with those in the wild-type mice.

Conclusions

The findings suggested that the acute hypoxia exposure could trigger the activation of Nrf2-ARE pathway, with longer duration associated with higher responses, and HIF-1α expression might be involved in promoting the Nrf2-mediated antioxidant responses in skeletal muscle.

]]>
<![CDATA[Effects of cold on murine brain mitochondrial function]]> https://www.researchpad.co/article/5c12cf83d5eed0c4849147f5

Therapeutic hypothermia is a strategy that reduces metabolic rate and brain damage during clinically-relevant hypoxic events. Mitochondrial respiration is compromised by hypoxia, with deleterious consequences for the mammalian brain; however, little is known about the effects of reduced temperature on mitochondrial metabolism. Therefore, we examined how mitochondrial function is impacted by temperature using high resolution respirometry to assess electron transport system (ETS) function in saponin-permeabilized mouse brain at 28 and 37°C. Respirometric analysis revealed that, at the colder temperature, ETS respiratory flux was ~ 40–75% lower relative to the physiological temperature in all respiratory states and for all fuel substrates tested. In whole brain tissue, the enzyme maximum respiratory rates for complexes I-V were similarly reduced by between 37–88%. Complexes II and V were particularly temperature-sensitive; a temperature-mediated decrease in complex II activity may support a switch to complex I mediated ATP-production, which is considerably more oxygen-efficient. Finally, the mitochondrial H+-gradient was more tightly coupled, indicating that mitochondrial respiration is more efficient at the colder temperature. Taken together, our results suggest that improvements in mitochondrial function with colder temperatures may contribute to energy conservation and enhance cellular viability in hypoxic brain.

]]>
<![CDATA[Role of altered proteostasis network in chronic hypobaric hypoxia induced skeletal muscle atrophy]]> https://www.researchpad.co/article/5bae98fc40307c0c23a1c155

Background

High altitude associated hypobaric hypoxia is one of the cellular and environmental perturbation that alters proteostasis network and push the healthy cell towards loss of muscle mass. The present study has elucidated the robust proteostasis network and signaling mechanism for skeletal muscle atrophy under chronic hypobaric hypoxia (CHH).

Methods

Male Sprague Dawley rats were exposed to simulated hypoxia equivalent to a pressure of 282 torr for different durations (1, 3, 7 and 14 days). After CHH exposure, skeletal muscle tissue was excised from the hind limb of rats for biochemical analysis.

Results

Chronic hypobaric hypoxia caused a substantial increase in protein oxidation and exhibited a greater activation of ER chaperones, glucose-regulated protein-78 (GRP-78) and protein disulphide isomerase (PDI) till 14d of CHH. Presence of oxidized proteins triggered the proteolytic systems, 20S proteasome and calpain pathway which were accompanied by a marked increase in [Ca2+]. Upregulated Akt pathway was observed upto 07d of CHH which was also linked with enhanced glycogen synthase kinase-3β (GSk-3β) expression, a negative regulator of Akt. Muscle-derived cytokines, tumor necrosis factor-α (TNF-α), interferon-ϒ (IFN-©) and interleukin-1β (IL-1β) levels significantly increased from 07d onwards. CHH exposure also upregulated the expression of nuclear factor kappa-B (NF-κB) and E3 ligase, muscle atrophy F-box-1 (Mafbx-1/Atrogin-1) and MuRF-1 (muscle ring finger-1) on 07d and 14d. Further, severe hypoxia also lead to increase expression of ER-associated degradation (ERAD) CHOP/ GADD153, Ub-proteasome and apoptosis pathway.

Conclusions

The disrupted proteostasis network was tightly coupled to degradative pathways, altered anabolic signaling, inflammation, and apoptosis under chronic hypoxia. Severe and prolonged hypoxia exposure affected the protein homeostasis which overwhelms the muscular system and tends towards skeletal muscle atrophy.

]]>
<![CDATA[Both living bacteria and eukaryotes in the mosquito gut promote growth of larvae]]> https://www.researchpad.co/article/5b4a286a463d7e4513b897e9

We recently reported that larval stage Aedes aegypti and several other species of mosquitoes grow when living bacteria are present in the gut but do not grow when living bacteria are absent. We further reported that living bacteria induce a hypoxia signal in the gut, which activates hypoxia-induced transcription factors and other processes larvae require for growth. In this study we assessed whether other types of organisms induce mosquito larvae to grow and asked if the density of non-living microbes or diet larvae are fed obviate the requirement for living organisms prior results indicated are required for growth. Using culture conditions identical to our own prior studies, we determined that inoculation density of living Escherichia coli positively affected growth rates of Ae. aegypti larvae, whereas non-living E. coli had no effect on growth across the same range of inoculation densities. A living yeast, alga, and insect cell line induced axenic Ae. aegypti first instars to grow, and stimulated similar levels of midgut hypoxia, HIF-α stabilization, and neutral lipid accumulation in the fat body as E. coli. However, the same organisms had no effect on larval growth if heat-killed. In addition, no axenic larvae molted when fed two other diets, when fed diets supplemented with heat-killed microbes or lysed and heat-killed microbes. Experiments conducted with An. gambiae yielded similar findings. Taken together, our results indicate that organisms from different prokaryotic and eukaryotic groups induce mosquito larvae to grow, whereas no conditions were identified that stimulated larvae to grow in the absence of living organisms.

]]>
<![CDATA[Macrobenthic communities in a shallow normoxia to hypoxia gradient in the Humboldt upwelling ecosystem]]> https://www.researchpad.co/article/5b600f87463d7e3af00e5a8c

Hypoxia is one of the most important stressors affecting the health conditions of coastal ecosystems. In highly productive ecosystems such as the Humboldt Current ecosystem, the oxygen minimum zone is an important abiotic factor modulating the structure of benthic communities over the continental shelf. Herein, we study soft-bottom macrobenthic communities along a depth gradient–at 10, 20, 30 and 50 m–for two years to understand how hypoxia affects the structure of shallow communities at two sites in Mejillones Bay (23°S) in northern Chile. We test the hypothesis that, during months with shallow hypoxic zones, community structure will be much more dissimilar, thereby depicting a clear structural gradient with depth and correlated abiotic variables (e.g. organic matter, temperature and salinity). Likewise, during conditions of deeper hypoxic zones, communities will be similar among habitats as they could develop structure via succession in conditions with less stress. Throughout the sampling period (October 2015 to October 2017), the water column was hypoxic (from 2 to 0.5ml/l O2) most of the time, reaching shallow depths of 20 to 10 m. Only one episode of oxygenation was detected in June 2016, where normoxia (>2ml/l O2) reached down to 50 m. The structure of the communities depicted a clear pattern of increasing dissimilarity from shallow normoxic and deep hypoxic habitat. This pattern was persistent throughout time despite the occurrence of an oxygenation episode. Contrasting species abundance and biomass distribution explained the gradient in structure, arguably reflecting variable levels of hypoxia adaptation, i.e. few polychaetes such as Magelona physilia and Paraprionospio pinnata were only located in low oxygen habitats. The multivariable dispersion of community composition as a proxy of beta diversity decreased significantly with depth, suggesting loss of community structure and variability when transitioning from normoxic to hypoxic conditions. Our results show the presence of semi-permanent shallow hypoxia at Mejillones Bay, constraining diverse and more variable communities at a very shallow depth (10–20 m). These results must be considered in the context of the current decline of dissolved oxygen in most oceans and coastal regions and their impact on seabed biota.

]]>
<![CDATA[Loss of ATP-Sensitive Potassium Channel Surface Expression in Heart Failure Underlies Dysregulation of Action Potential Duration and Myocardial Vulnerability to Injury]]> https://www.researchpad.co/article/5989da9bab0ee8fa60ba3dbc

The search for new approaches to treatment and prevention of heart failure is a major challenge in medicine. The adenosine triphosphate-sensitive potassium (KATP) channel has been long associated with the ability to preserve myocardial function and viability under stress. High surface expression of membrane KATP channels ensures a rapid energy-sparing reduction in action potential duration (APD) in response to metabolic challenges, while cellular signaling that reduces surface KATP channel expression blunts APD shortening, thus sacrificing energetic efficiency in exchange for greater cellular calcium entry and increased contractile force. In healthy hearts, calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylates the Kir6.2 KATP channel subunit initiating a cascade responsible for KATP channel endocytosis. Here, activation of CaMKII in a transaortic banding (TAB) model of heart failure is coupled with a 35–40% reduction in surface expression of KATP channels compared to hearts from sham-operated mice. Linkage between KATP channel expression and CaMKII is verified in isolated cardiomyocytes in which activation of CaMKII results in downregulation of KATP channel current. Accordingly, shortening of monophasic APD is slowed in response to hypoxia or heart rate acceleration in failing compared to non-failing hearts, a phenomenon previously shown to result in significant increases in oxygen consumption. Even in the absence of coronary artery disease, failing myocardium can be further injured by ischemia due to a mismatch between metabolic supply and demand. Ischemia-reperfusion injury, following ischemic preconditioning, is diminished in hearts with CaMKII inhibition compared to wild-type hearts and this advantage is largely eliminated when myocardial KATP channel expression is absent, supporting that the myocardial protective benefit of CaMKII inhibition in heart failure may be substantially mediated by KATP channels. Recognition of CaMKII-dependent downregulation of KATP channel expression as a mechanism for vulnerability to injury in failing hearts points to strategies targeting this interaction for potential preventives or treatments.

]]>
<![CDATA[Role of Alanine Dehydrogenase of Mycobacterium tuberculosis during Recovery from Hypoxic Nonreplicating Persistence]]> https://www.researchpad.co/article/5989d9f5ab0ee8fa60b6fdc1

Mycobacterium tuberculosis can maintain a nonreplicating persistent state in the host for decades, but must maintain the ability to efficiently reactivate and produce active disease to survive and spread in a population. Among the enzymes expressed during this dormancy is alanine dehydrogenase, which converts pyruvate to alanine, and glyoxylate to glycine concurrent with the oxidation of NADH to NAD. It is involved in the metabolic remodeling of M. tuberculosis through its possible interactions with both the glyoxylate and methylcitrate cycle. Both mRNA levels and enzymatic activities of isocitrate lyase, the first enzyme of the glyoxylate cycle, and alanine dehydrogenase increased during entry into nonreplicating persistence, while the gene and activity for the second enzyme of the glyoxylate cycle, malate synthase were not. This could suggest a shift in carbon flow away from the glyoxylate cycle and instead through alanine dehydrogenase. Expression of ald was also induced in vitro by other persistence-inducing stresses such as nitric oxide, and was expressed at high levels in vivo during the initial lung infection in mice. Enzyme activity was maintained during extended hypoxia even after transcription levels decreased. An ald knockout mutant of M. tuberculosis showed no reduction in anaerobic survival in vitro, but resulted in a significant lag in the resumption of growth after reoxygenation. During reactivation the ald mutant had an altered NADH/NAD ratio, and alanine dehydrogenase is proposed to maintain the optimal NADH/NAD ratio during anaerobiosis in preparation of eventual regrowth, and during the initial response during reoxygenation.

]]>